The present invention relates to a liquid crystal display cell and, more particularly, it relates to a liquid crystal display cell in which a liquid crystal material is sandwiched between a pair of flexible polymer film substrates having a specific transparent electrode disposed on the surface thereof.
In liquid crystal display cells, those having transparent conductive films (transparent electrodes) formed on the surface of a substrate made of a high melting material such as glass or quartz, have often been used generally. In the case of using such a high melting substrate, since the transparent electrode film can be formed at a relatively high temperature (higher than 150.degree. C.), the thus formed transparent conductive film is highly crystalline and has great toughness. In addition, upon manufacturing a liquid crystal cell, since the substrate is rigid, the substrate is not bent during the manufacturing steps and as a result, no cracks are formed in the transparent electrode.
Along with a recent trend in the liquid crystal display cell of reducing the weight and the thickness, it has been attempted to replace the high melting substrate such as glass with a synthetic resin substrate (in particular, a flexible polymer film substrate). For instance, it has been proposed a liquid crystal display cell produced by using a synthetic resin film as a substrate and forming a transparent conductive film made of a metal oxide such as ITO, indium oxide, tin oxide or antimony oxide on the flexible synthetic resin substrate (refer, for example, to Japanese Patent Publication (KOKOKU) No. 62-3929, Japanese Patent Application Laid-Open (KOKAI) Nos. 62-187324 and 63-18327).
In the liquid crystal display cell using the flexible polymer film as the substrate, however, since the substrate is flexible, the resistivity is increased due to the occurrence of cracks in the transparent electrode during the manufacturing steps of the liquid crystal display cell, or cracks arise in the transparent electrode by pressurizing or heating upon connection with a driving circuit, thereby bringing about an undesirable phenomenon of display defect at present. The phenomenon becomes more conspicuous as the resistivity of the transparent electrode is lower and the film thickness of the transparent electrode is greater, and as a result, the yield of the liquid crystal display reduces.
Recently, the liquid crystal display using the flexible film substrate has been required to provide more fine and accurate display, high display-capacity and large display-area, and accordingly, the suppression of the occurrence of cracks in the transparent electrode is demanded.
As a result of an earnest study for providing a liquid crystal display of more fine and accurate display, high display-capacity and large display-area by using a flexible polymer film substrate and with no occurrence of cracks in the transparent electrode formed on the substrate, it has been found that a metal-oxide film formed on a polymer film substrate by means of a specified sputtering method, vacuum vapor deposition method or ion plating method based on the following knowledges, which the metal-oxide film has a surface resistivity of not greater than 100 ohm/.quadrature. and is substantially amorphous, is able to dissolve the foregoing technical subjects:
(1) it is required for the liquid crystal display having a high display-capacity to reduce the surface resistance for the resistivity of the transparent conductive film to not greater than 100 ohm/.quadrature., but the formation of a liquid crystal display cell becomes extremely difficult in view of the occurrence of cracks of the transparent conductive film and the occurrence of curling in the substrate in the case of reducing the surface resistivity to not greater than 100 ohm/.quadrature.;
(2) as a result of X-ray analysis for ITO films often used generally as the transparent electrode, the crystallization occurs even in the ITO film having the surface resistivity of not greater than 100 ohm/.quadrature. on the flexible polymer film substrate like that in the ITO film on the glass substrate (on the contrary, the ITO film having the surface resistivity of 200 to 300 ohm/.quadrature. on the flexible polymer film substrate is substantially amorphous); and
(3) in view of the relationship between the crystallinity in the ITO film and the bending property (Note (3) described later), curling property (Note (4) described later) and the etching property (Note (5) described later) of the ITO film, these three properties are all worsened as the crystallization is higher. Based on the finding, the present invention has been attained.